INTRODUCTION: Snake envenomings are a health problem in rural areas of tropical and subtropical countries, but little is known regarding the immune response presented by bitten individuals. The IgM production of patients bitten by Bothrops erythromelas snake was analyzed to identify the effectiveness of treatment in this type of envenomation.METHODS: Bothrops erythromelas venom was submitted to electrophoresis and transferred to a nitrocellulose sheet, following incubation with patients' sera.RESULTS: A 38 KDa protein was detected before and 24 h after therapy.CONCLUSIONS: The result suggests that this protein could be used as a marker for individuals envenomed by Bothrops. erythromelas.